Generating Flow Frequencies

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Generating Flow Frequencies Updating NOAA
Atlas Precipitation Frequency for California

by John High, Hydrologist Sacramento
District U.S. Army Corps of Engineers
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Precipitation Frequency Curves also
called Depth Duration Frequency (DDF)
Curves Q What are they used for?? A Input
to Rational Equation or Rainfall-Runoff Model
Calculate peak discharge - channel
design - levee design - culvert
design - floodplain mapping
Calculate a runoff volume for a storage area or a
dam
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Watershed Map
Damage reach
Streamgage
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1. Create Rainfall-Runoff Model Calibrate to
Historic Storm Event

Concentration point
Damage reach
streamgage
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1983 FLOOD
RAINFALL IN INCHES PER HOUR
PEAK 53,500 CFS
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1. Input design storm into model and adjust
   parameters to match flow frequency curve.

Concentration point
Damage reach
streamgage
hydrograph
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Flow Frequency Curve
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Concentration point
Damage reach
streamgage
100-yr design hydrograph
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Existing Depth-Duration Frequency Curves for
California - NOAA ATLAS 2 Precipitation
Frequency Atlas of the Western United States,
Vol XI- California, 1973 - Department of Water
Resources Rainfall Analysis for Drainage
Design Bulletin 195, 1976 (regional
frequency analysis by Jim Goodridge and staff)

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• NOAA Atlas 2
• 1. Covers 11 Western States
• 2. Regional Frequency Analysis
• Gumbel Extreme Value Distribution
• Isopluvial Maps for 6-hr and 24-hr duration, 2
  100 yr return periods
• Use formulas/charts to derive other
• durations/return periods
• 6. GIS maps recently available in raster format
  (cells)

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NOAA Atlas 2
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• DWR Bulletin 195
• 1. Covers California
• 2. Regional Frequency Analysis
• Pearson Normal Distribution
• Hard-copy maps of 2-yr thru 10,000 yr, short and
  long-duration values
• Analyzed 2,000 gages
• Note DWR will update Bulletin 195 near future.
  GIS map layers available within a couple years
• - David Rizzardo of DWR

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WHY HASNT NOAA ALTAS 2 BEEN UPDATED?

• NOAA Atlas updates are NOT in the Weather
  Services Mission Statement
• U.S. Congress provides no funding
• Funding must come from other federal or state
  agencies

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UPDATED PORTIONS OF THE COUNTRY

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WHO DOES THE UPDATE?

• National Weather Service    Hydrometeorological
  Design Studies Center    Silver Spring, MD  
  Geoff Bonnin, Chief
• Small, top-notch team of scientists.
• Future funding uncertain, so staff may be laid
  off.

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• Funding to Finish NOAA14 for California
• Total Cost 305,000 -or- more
• 1. CALTRANS 100,000
• Glenn Decou, Chief of Highway Drainage Design
• 2. CA Department of Water Resources 100,000
• 3. NWS, Sacramento Office (Coastal Storms
  Program) maybe 50,000?
• U.S. Army Corps of Engineers 55,000 or more
• COMPLETED PRODUCT IN 2 3 YEARS

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LOCATION ON EAST SIDE OF LAKE TAHOE 90
Confidence Interval Upper Bound 5.53
inches 100YR, 24-HOUR DEPTH
4.93 inches 90 Confidence Interval Lower
Bound 4.32 inches
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• SUMMARY
• The National Weather Service will start work on
  NOAA14 for the rest of California within a few
  months.
• Completion will be in 2 3 years
• Study will incorporate state-of-the-art methods
  and technology
• Includes quality control and screening not all
  gages will be used
• Study will include review and comment period of
  draft product
• Concern NWS used calendar year analysis of data
  for Semi-Arid region. Not appropriate for
  California annual data should be separated by
  Water Year.

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Weblink for NWS NOAA14 Precipitation http//hdsc
.nws.noaa.gov/hdsc/pfds/index.html Points of
Contact Dave Rizzardo, DWR 916-574-2617 John
High, USACE 916-557-7136 THE END